1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, such as a multifunction machine or a copier. More particularly, the present general inventive concept relates to an automatic document feeder of an image forming apparatus having a duplex printing function.
2. Description of the Related Art
Generally, an image forming apparatus, such as a multifunction machine, a copier, or the like, is provided with an automatic document feeder, which continuously and automatically feeds a document to be scanned onto a document scanning part of a scanner unit. The automatic document feeder usually has a single scan path, and a duplex scan path to reverse the document, one surface of which is scanned, and to admit(feed) the reversed document to the document scanning part.
FIG. 1 illustrates a conventional automatic document feeder. Referring to FIG. 1, reference numerals 1, 2, 10 and 20 represent a document feeder frame, a document scanning part, a single scan path, and a duplex scan path, respectively.
The single scan path 10 is provided with a document admission passage 12 to admit or feed a document D of a document supplying tray 11 to the document scanning part 2 and a document discharge passage 13 to discharge the scanned document. The duplex scan path 20 is connected from the document discharge passage 13 to the single scan path 10 at front of the document scanning part 2. In FIG. 1, reference numerals 14-17 and 21 represents document conveying rollers.
In a single printing mode, the document D is scanned passing through in turn, paths {circle around (a)}, {circle around (b)}, {circle around (c)}, {circle around (d)}, {circle around (e)}, and {circle around (f)} whereas in a duplex printing mode, the document D, both surfaces of which are scanned passing through the single scan path as described above, is scanned and discharged in a state that it is reversed passing through paths {circle around (a)}, {circle around (b)}, {circle around (c)}, {circle around (d)}, {circle around (e)}, and {circle around (f)}.
If the document having the both surfaces scanned is discharged through the duplex scan path 20 in the duplex printing mode, it requires that the document is discharged in a state that it is collated in the same page as that in an admission thereof in the document admission passage 12. For this, before being discharged, the document having the both surfaces scanned is to pass through the duplex scan path (paths {circle around (g)}, {circle around (h)}, {circle around (c)}, {circle around (d)}, {circle around (e)}, and {circle around (f)}) again.
As described above, in the duplex printing mode, after the preceding document is completely discharged passing through {circle around (a)}, {circle around (b)}, {circle around (c)}, {circle around (d)}, {circle around (e)}, {circle around (f)}, {circle around (g)}, {circle around (h)}, {circle around (c)}, {circle around (d)}, {circle around (e)}, {circle around (f)}, {circle around (g)}, {circle around (h)}, {circle around (c)}, {circle around (d)}, {circle around (e)}, and {circle around (f)} in turn, the following document is to be admitted into the document admission passage 12. Accordingly, a printing efficiency in the duplex printing mode is very low. In this case, the printing efficiency is no more than approximately 40% of that in the single printing mode.
To increase the printing efficiency in the duplex printing mode, a method is employed to shorten the duplex scan path and move a conveying roller away from a corresponding backup roller at a place where the documents overlaps each other. In this case, however, to collate and discharge the document having the both surfaces scanned, the document should pass through the duplex scan path again. Accordingly, there is a limit to increase the printing efficiency.